I just wanted to chime in here and mention that we're *always* looking at the performance of the game, including the UI. It's never something we push to the side.

One thing to keep in mind though when you turn off the UI with control+U you're not just turning off the UI, you're turning off any logic that has to deal with displaying it, so there will always be some frame gain by doing that.

We have some ideas we're looking into for UI performance improvements now; nothing definite yet. It is something we're always keeping in mind and looking at ways to improve it.